how can I get refresh token

The acquiretokenbyrefreshtoken function is available in ADAL 2.X , that code sample is using ADAL 3.13.8 , and from ADAL3.X, library won't expose refresh token and AuthenticationContext.AcquireTokenByRefreshToken function.

ADAL caches refresh token and will automatically use it whenever you call AcquireToken and the requested token need renewing(even you want to get new access token for different resource).

please see the explanation from here . Also click here and here for more details about refresh token in ADAL .

If you looking for a persistent mechanism, you can simply use TokenCache.Serialize()

Here's how I did it:

First, get the token and serialize the cache token

AuthenticationContext authContext = new AuthenticationContext($"https://login.microsoftonline.com/{Tenant}");
var authResult = authContext.AcquireTokenAsync(resource, ClientId, new Uri("https://login.microsoftonline.com/common/oauth2/nativeclient"), new PlatformParameters(PromptBehavior.SelectAccount)).Result;
byte[] blobAuth = authContext.TokenCache.Serialize();

Then, load the cached bytes

AuthenticationContext authContext = new AuthenticationContext($"https://login.microsoftonline.com/{tenant}/");
authContext.TokenCache.Deserialize(blobAuth);
var res = authContext.AcquireTokenSilentAsync(resource, clientId).Result;